Properties of light

[EWright]

There are a few questions I have regarding the properties of light; specifically properties of a single photon.

 

If I have a device that emits a single visible photon towards an observer who is able to see that photon arrive... will I also be able to view that single visible photon since it is traveling away from me?

 

Secondly, would the single photon lose intensity based on the distance to my observer, in accordance with the inverse square law?

 

Is a photon considered 3-dimensional?

 

The wave associated with a photon is often depicted as a two dimensional linear wave. Is this an accurate depiction, or is is more three dimensional as well?

[Tormod]

There are a few questions I have regarding the properties of light; specifically properties of a single photon.

 

If I have a device that emits a single visible photon towards an observer who is able to see that photon arrive... will I also be able to view that single visible photon since it is traveling away from me?

 

No. If you emit one photon, you have created an electromagnetic wave moving at the speed of light towards your observer. You cannot see it since the photon in itself does not emit light in your direction, it is a fundamental particle.

 

Secondly, would the single photon lose intensity based on the distance to my observer, in accordance with the inverse square law?

 

No, the photon does not lose "intensity". Depending on the distance to your observer it might get redshifted, though.

 

Is a photon considered 3-dimensional?

 

The wave associated with a photon is often depicted as a two dimensional linear wave. Is this an accurate depiction, or is is more three dimensional as well?

 

Both the particle and the wave descriptions must be taken as simplified versions of "reality". A photon travels as a wave and only behaves as a particle when it interacts with another particle.

[Drip Curl Magic]

wow, all of that just went right over my head. It's times like these that I wish I hadn't been so rebelious during highschool. Then maybe I'd have a better grasp on some of this.

[Tarantism]

wow, all of that just went right over my head. It's times like these that I wish I hadn't been so rebelious during highschool. Then maybe I'd have a better grasp on some of this.

im right there with ya, drippy.

[arkain101]

Imagine light like this. If you have a thousand ping pong balls floating on a calm pond. We consider those atoms. They are all stuck together forming a round shape, perfectly still. Now, we take another ping pong ball and excite it, we pick it up and drop it in the water. we imagine it makes a decent sized wave, and we imagine the ping ping ball we dropped is actually a ping pong ball and full of atoms. It emmits light in all directions. Now when the wave comes to the circular collection of attoms it disturbes them at a cirtain frequency and amplitude. Now some of those waves are absorbed and some are reflected out in different directions. The waves actually also push back the atoms a little each wave. This analogy is far from how things really work but it shows how a electromagnetic distubance is only visible if it is able to interact with matter and give it a buzz, which in turn, excites atoms in our retina, either electrically or heat wise not sure, and our brain interprets it.

 

Alright EWright, I have some question to add to this aswell.

 

-What does the device that "measures" an electromagnetic wave do in order to process a 2 dimensional wave imagination of it, with changing frequencies and amplitued? There is center of the wave, which I take is the relaxed no energy state, then there is a top peak and a bottom peak. Are the different peaks different in characteristics? or are the simply raises of energy displayed on a machine as a wave form?

It would make sense to create a machine that drew a wave on a moniter, not unlike a sound recording program that displays a wave from the sound it hears.

So did this wave idea come from drawing visual interpratation of the characteristics light has.? kinda like sound?

For example, if we have a machine that draws a wave when objects hit a absorbtion plate connected to a sensor, and we shoot this plate with a small caliber machine gun, and we imagine the bullits are photons, and we fire at 1000round per minute. The frequency that the bullets hit the plate should draw the wavelength on the moniter on the screen, displaying the frequency, and the actual weight or energy of the bullet should draw the amplitude. Would this be a good example of how "light" is considered a wave to understand with more clarity?

where a bigger caliber or more massive bullet would increase amiplitude and rpm would change frequency. and the non polarization of the light is from light being reflected in slightly different directions from particles in its path, which would we would imagine the bullets relfecting off of tiny strings in its path scattering the aim a little. creating the effect of glare like when light is messy as it comes off a lake its frequencies get messy and make it a little bit whiter and the polarized glasses even it out again? hope that all makes sense.

[erKa]

Reply 1

No if the "photon " has only a frontward way of transmission, like a "wavy" bullet. Even if a visible photon must have wavelength and wavefront about 500 nanometers length.True visible light.

Reply 2

No. there is a redshift visible from target only if emitter is running away from it or a blueshift if the emitter is moving towards the target. This is the way the motion of stars is calculated. But if 2 stars are always at the same distance everyone looks the other without any chromatic shifting.The photon is a "boson" (from Bose) particle having no rest mass and it can move in ordinary space in any allowable direction, like a bullet. But it can exist only at "c" speed, so there is no inverse square law of the decay because the all the photons produced still stand somewhere in the universe, also those produced during Big Bang.

Reply 3

If the photon is moving wavy but lying on a fixed plane it is "polarized". Polarization is an allowable mode of transmission. Buy Polaroid goggles and you will taste the polarization of light!

[arkain101]

Reply 2

No. there is a redshift visible from target only if emitter is running away from it or a blueshift if the emitter is moving towards the target. This is the way the motion of stars is calculated. But if 2 stars are always at the same distance everyone looks the other without any chromatic shifting.

 

How is red shift explained? If I am moving away from a light source really fast it turns more red? If anything changes whatsoever with the property of light in relation to ones velocity, shouldnt that destroy the theory of light being the same velocity in all reference frames, where time is the modifier to make up for the apparent constant?

 

I really wonder about this. Since, red is a lesser frequency, it makes sense that if you are capable to run from light (proving its not a constant) then the frequency it hits you might slightly decrease.

[Tormod]

Keep in mind that we are talking about a single photon, not a beam of light. Thus it cannot be detected by anything except a photon detector, and it has to pass through it. A single photon would not *very rarely* even register in our eyes.

 

A little info:

http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html

[Tormod]

How is red shift explained? If I am moving away from a light source really fast it turns more red? If anything changes whatsoever with the property of light in relation to ones velocity, shouldnt that destroy the theory of light being the same velocity in all reference frames, where time is the modifier to make up for the apparent constant?

 

This is *explained* by relativity, not contradicting it.

 

The frequency gets redshifted (or blueshifted) depending on whether the source of light is moving towards you or away from you. The photon does not travel faster or slower.

 

The apparent redshifting of almost all galaxies (as seen from our point of view) is what lead Hubble to conclude that our universe is expanding.

[Erasmus00]

There are a few questions I have regarding the properties of light; specifically properties of a single photon.

 

If I have a device that emits a single visible photon towards an observer who is able to see that photon arrive... will I also be able to view that single visible photon since it is traveling away from me?

 

No.

 

Secondly, would the single photon lose intensity based on the distance to my observer, in accordance with the inverse square law?

 

Visible light spreads out proportionally to an inverse square law only when you have some form of spherical symmetry. It takes spherical waves or an ensemble of linear waves to create an inverse square power law. One photon will simply carry its energy away in a straight line untill it hits or gets deflected by something.

 

 

Is a photon considered 3-dimensional?

 

The photon could, I guess, be considered to have a span equal to the spread of its waveform. It could also be thought of as a point particle being "carried" by its waveform.

 

The wave associated with a photon is often depicted as a two dimensional linear wave. Is this an accurate depiction, or is is more three dimensional as well?

 

It depends on the polarization of light and the way in which it is traveling. For light traveling in a straight line in free space, we can think of the light as two perpendicular plane waves, one an oscillating E field, one an osciallting B field.

-Will

[arkain101]

The photon in relatation to space-time does not travel faster or slower I know. But if the frequency is able to change, it would sound very logical that its constant speed is coming at us at different velocities, but, it is always going C but its source is changing points of origin.

 

Unless there is some kind of time dialation involved here.

[erKa]

How is red shift explained? If I am moving away from a light source really fast it turns more red? If anything changes whatsoever with the property of light in relation to ones velocity, shouldnt that destroy the theory of light being the same velocity in all reference frames, where time is the modifier to make up for the apparent constant?

 

I really wonder about this. Since, red is a lesser frequency, it makes sense that if you are capable to run from light (proving its not a constant) then the frequency it hits you might slightly decrease.

Doppler's effect must be applied to the light beam ( a sequence of photons emitted in a direction both verses), a single photon must be considered only a wavy bullet obliged to move at "c" speed. The observer on the emitter has no sight of the fired bullet, the observer on the target will be hit by a wavy bullet "c" fast without any preview of it. A simple relativistic ballistic problem.

[EWright]

Doppler's effect must be applied to the light beam ( a sequence of photons emitted in a direction both verses), a single photon must be considered only a wavy bullet obliged to move at "c" speed. The observer on the emitter has no sight of the fired bullet, the observer on the target will be hit by a wavy bullet "c" fast without any preview of it. A simple relativistic ballistic problem.

 

In explaining this for a single photon, you do not address the prior poster's question of explaining redshift. I beleive he's trying to understand, why, if each single photon is traveling away at a constant speed, the beam of the whole becomes redshifted if they're all traveling (presumably) in the same direction with the same speed.

[phision]

red/blueshift? has the energy of a photon, involved in red or blue-shift, actually changed? if so where has the energy gone? if not why has the colour changed?

 

Also, I know photons interact with electrons, but do they interact with each other or other particles? what are these interactions?

 

do single photons have wave properties?

[CraigD]

Some quick, standard answers, obtainable from nearly any science education website or textbook:

red/blueshift? has the energy of a photon, involved in red or blue-shift, actually changed?

Yes. By any measure, such as it’s ability to, say, heat water, a blueshifted photon (one who’s source and receiver are moving toward one another) has more energy than a photon proton produced by its source of exactly the same energy by precisely the same means that is redshifted (its source and receiver moving away from it)

if so where has the energy gone?

It hasn’t, in an absolute sense, gone anywhere.

 

Consider the difference between being bumped on a ski slope by someone skiing beside you, vs. being slammed into the same skier while you’re standing still. Clearly, the same skier, moving at the same speed relative to the surface of the ski slope, has different kinetic energies when colliding with you at different relative speeds.

 

By analogy, light is similar.

Also, I know photons interact with electrons, but do they interact with each other or other particles?

Bosons – which include photons – don’t interact with one another. They do interact with fermions, which include electrons.

 

Technically, this lack of interaction is described by Bose–Einstein statistics

do single photons have wave properties?

Yes.

 

This surprising experimental result, conventionally known as the double slit, or Young’s, experiment, is one of the cornerstones of modern physics.

[Little Bang]

Ewright, imagine yourself standing on a beach next the edge of the water, no moon, no stars and no light for you to see. There is no wind and the ocean is perfectly calm as for as you can tell. A small asteroid hits the ocean about hundred meters away from you and causes a one meter wave that starts propagating toward you. When the wave hits all you will detect is a very small piece of the total energy output of that asteroid impact. The production of light is very similar to this scenario. It is impossible to produce a single photon. Please see, http://hypography.com/forums/strange-claims-forum/22596-photon-creation.html

[Jay-qu]

Bosons – which include photons – don’t interact with one another. They do interact with fermions, which include electrons.

 

Beautiful answer as always Craig, but I must nit-pick right here. Bosons can and do interact with one another - in non-abelian gauge theories such as quantum chromodynamics we have coupling terms between the gluons - so gluons which are bosons interact with each other. Electromagnetism is an abelian gauge theory which has no couplings between photons, so like you said they dont interact with each other.